Passive thermal control is desired in a variety of settings where thermal dissipaters are associated with equipment having a narrow temperature range in which to function. In this context, passive thermal control systems include systems that substantially automatically dissipate heat through conduction, convection and/or radiation without the active involvement of complicated temperature feedback control components or other potentially costly, complex, massive or less reliable mechanisms.
The case of thermal management of systems for spacecraft including satellites is illustrative. Such systems may include large, typically planar solar arrays, batteries, sensitive instruments, large, typically planar antennae and associated electronics. Many of these components require a narrow range of operating temperatures for optimal performance. Preferably, such systems employ passive thermal control, involving radiating heat into cold space, to maintain thermal stability such that active control systems, with attendant complexity, added mass and potential for malfunction, are not required.
In this regard, it is typically desired to maintain antenna electronics in a temperature range of between about +40° C. and −40° C. Some other components that spacecraft designers would like to use, if they could be accommodated, optimally require an even narrower temperature range. For example, spacecraft designers have recognized that Lithium-based batteries (e.g., Lithium ion, Lithylene, etc.) provide a number of potential advantages for spacecraft applications because they offer lighter, more efficient assemblies. However, such batteries require a narrow operating temperature range for optimal performance, for example, an operating range between about +30° C. and −15° C. Such batteries typically also require limited depth of discharge and careful charge control to more fully realize their potential benefits for spacecraft applications.
In the spacecraft environment, a number of obstacles complicate passive thermal control. First, there are typically tremendous and greatly varying thermal dissipation requirements. The magnitude of such heat dissipation may be the result of, for example, the operation of many components in a small volume and high solar fluxes on radiation attenuating surfaces. Substantial variability and heat dissipation requirements may be the result of varying operating modes of instruments (and attendant variations in RF and DC power consumption) based on mission objectives, varying solar energy fluxes as a function of orbital phase, and varying beta angles (the angle of the solar vector to the orbital plane) as between different missions. Accordingly, one challenge that faces designers in such contexts is providing temperature control to within a narrow range in a challenging thermal environment using passive thermal control. Another challenge relates to providing thermal control and other control necessary to realize the potential advantages of preferred components such as Lithium-based batteries. Some of the many other challenges include meeting mission requirements for size and mass, simplifying control systems, improving manufacturability, and enabling orbital and other operating parameters that have previously been unattainable or impractical due to limitations related to thermal control, energy storage, charge control, power distribution and other systems.